A few thoughts from John Fleck, a writer of journalism and other things, living in New Mexico

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Brad Udall’s western water climate change bibliography

Speaking earlier this month at the University of Colorado’s Martz Conference, Brad Udall offered what amounted to a bibliography, both helpful and deeply unnerving, of recent scientific literature documenting what we have learned in recent years about climate change and water in the Western United States, and what it tells us about our future prospects.

Mote, Philip W., et al. “Perspectives on the causes of exceptionally low 2015 snowpack in the western United States.” Geophysical Research Letters 43.20 (2016).

….both human influence and sea surface temperature (SST) anomalies contributed strongly to the risk of snow drought in Oregon and Washington: the contribution of SST anomalies was about twice that of human influence. By contrast, SSTs and humans appear to have played a smaller role in creating California’s snow drought. In all three states, the anthropogenic effect on temperature exacerbated the snow drought.

Mann, Michael E., and Peter H. Gleick. “Climate change and California drought in the 21st century.” Proceedings of the National Academy of Sciences 112.13 (2015): 3858-3859.

….the increasing co-occurrence of dry years with warm years raises the risk of drought despite limited evidence of a trend in precipitation itself, highlighting the critical role of elevated temperatures in altering water availability and increasing overall drought intensity and impact.

In years of low precipitation, very low runoff ratios are made 2.5–3 times more likely by high temperatures. This temperature sensitivity appears to have strengthened in recent decades, implying future water management vulnerability should recent warming trends in the region continue.

Observations and reanalyses indicate that between the 1980s and 2000s, there was a 10–20% loss in the annual maximum amount of water contained in the region’s snowpack. Here we show that this loss is consistent with results from a large ensemble of climate simulations forced with natural and anthropogenic changes, but is inconsistent with simulations forced by natural changes alone. A further loss of up to 60% is projected within the next 30 years.

….recent droughts have been amplified by warmer temperatures that exacerbate the effects of relatively modest precipitation deficits. Since 1988, a marked increase in the frequency of warm years with lower flows than expected, given precipitation, suggests continued warming temperatures will be an increasingly important influence in reducing future UCRB water supplies.

….we found a consistent relationship between watershed ET and temperature across the Sierra Nevada; this consistency implies a potential widespread reduction in water supply with warming, with important implications for California’s economy and environment.

….desiccation is consistent across most of the models and moisture balance variables, indicating a coherent and robust drying response to warming despite the diversity of models and metrics analyzed. Notably, future drought risk will likely exceed even the driest centuries of the Medieval Climate Anomaly (1100–1300 CE) in both moderate (RCP 4.5) and high (RCP 8.5) future emissions scenarios, leading to unprecedented drought conditions during the last millennium.